At present, lithium-ion batteries have advantages of high energy density, high power density, longer cycle life and longer storage life. Thus, lithium-ion batteries have been widely applied in portable electronic devices such as mobile phones, digital cameras and portable computers, and also have wild application prospect in electric transportation vehicles such as electric vehicles and electric bicycles, as well as large-and-middle-sized electronic equipment such as energy storage facilities. The lithium-ion battery has become a key point to solve global problems such as energy crisis and environment pollution.
With the increasing improvement of the electric vehicle techniques, electric vehicles and hybrid vehicles become more and more closer to people's life, which brings huge business opportunities and, at the same time, higher demands on the safety performance of the lithium-ion batteries which provide energy for the electric vehicles. Generally, in order to effectively guarantee safety performance of a cell, the cell should have the following functions:
1) the first electrode assembly is electrically connected with the top cover plate;
2) the top cover plate is provided with a safety device, and the deformable plate provided on the top cover plate deforms when the pressure of the internal gas generated in the cell reaches a certain value, so that the first electrode assembly is electrically connected with the second electrode assembly, so as to form an external short circuit of the cell and effectively prevent overcharge of the cell.
However, since components which can realize these functions are arranged, a series of new problems arise in the top cover plate structure for power battery.
Generally, when the deformable plate deforms, the space between the deformable plate and the connecting block will be reduced. If the space is sealed, the air pressure therein will be increased, which influences the pressure value for normal deformation of the deformable plate and increases safety risk of the cell.
On the other hand, during the production of the cell, particularly during liquid injection and formation, it is unavoidable that there are some electrolyte residues around the electrode terminal. Particularly, when the electrolyte residues are excessive, if these electrolyte residues flow into the deformable plate and electrically connect the connecting block with the deformable plate, there will exist the risk of forming an external short circuit during normal use of the cell.
Additionally, the second electrode terminal is usually sealedly insulated from and fixed with the top cover plate by means of an insulating piece for electrode terminal. However, in some situations, the insulating piece for electrode terminal may loosen, age and get injured, leading to loss of sealing performance. Thus, those electrolytes may flow out from the gap between the connecting block and insulating piece and cause adverse consequence.
Moreover, since the top cover plate structure for power battery is small in size and has numerous components, if a corresponding structure is separately disposed in order to solve a specific problem, the structural complexity and assembling difficulties will be significantly increased. Therefore, it is an urgent need to provide a top cover assembly for power battery which can avoid all the above-mentioned problems at the same time.